[Effect of long-term incubation of spermatozoa on their thermal resistance and thermal selection].

A study was made of changes in the heat resistance of spermatozoa during their incubation in Ringer's solution, using two species of frogs (Rana temporaria and R. ridibunda) and of bivalve molluscs (Unio crassus and U. tumidus). The decrease in the heat resistance of spermatozoa is the more significant the longer energetic expenditures for their movements in the solution. Changes in the heat resistance are stochastic, and therefore the resistance levels at different terms of incubation are not correlated with the initial one. This is the reason for disappearance of correlation between the resistance of spermatozoa and that of somatic cells of a developing organism observed prior to incubation. Thus, selection of spermatozoa whose resistance determines that of somatic cells is substituted by a non-directed elimination of genotypes, i. e. thermal selection of spermatozoa becomes ineffective.